Conversion of dithioacetals

Cyanogen Iodide (ICN) has been used extensively for the cyanation of alkenes and aromatic compounds [12], iodination of aromatic compounds [13], formation of disulfide bonds in peptides [14], conversion of dithioacetals to cyanothioacetals [15], formation of trans-olefins from dialkylvinylboranes [16], lactonization of alkene esters [17], formation of guanidines [18], lactamization [19], formation of a-thioethter nitriles [20], iodocyanation of alkenes [21], conversion of alkynes to alkyl-iodo alkenes [22], cyanation/iodination of P-diketones [23], and formation of alkynyl iodides [24]. The products obtained from the reaction of ICN with MFA in refluxing chloroform were rrans-16-iodo-17-cyanomarcfortine A (14)... 

The reactive carbonyl of an aZde%do-sugar acetate adds thiols and from such adducts have been obtained mixed acetal and thioacetal derivatives 41, 4S) which are the probable intermediates in the Conversion of dithioacetals to furanosides (p. 199). 

Another indirect method is conversion of the aldehyde or ketone to a dithioacetal or ketal, and desulfurization of this (14-34). 

The conventional conversion of carbonyl systems by sulphur tetrafluoride into difluoroalkyl compounds has been modified in the reaction of dithioacetals with tetra-n-butylammonium dihydrogentrifluoride and A -bromo- or AModosuccinimide. Yields of the difluoroalkanes are generally in excess of 70% [35]. 

Acetals are usually easy to cleave by acid-catalyzed transacetalization or hydrolysis (Table 3.40). Dithioacetals, on the other hand, tend to be more resistant to hydrolysis, but cleavage can be achieved by treatment with mercury(II) salts or by oxidation with either [bis(trifluoroacetoxy)iodo]benzene [723] or periodic acid [724]. Use of the latter reagent can, however, also lead to the conversion of methyl ketones into iodo-methyl ketones [721],... 

The possibility of conversion of the dithioacctal into the corresponding ketone without reconjugation of the double bond is a noteworthy j feature of this synthetic scheme. The syntheses of iso-ar-turmerone and isoartemisia ketone mentioned above proceeded similarly via a carbophilic pathway. In the latter case a p-ethylenic dithioester was not isomerized during the following overall sequence carbophilic addition-methylation-dithioacetalization [343]. ... 

The conversion of dithioesters into aldehydes is also easily realized through reduction to a mixed dithioacetal by tributyltin hydride [264]. 

It has been demonstrated that reactions of ketene dithioacetals with suitable glycine derivatives provides convenient access to a variety of densely substituted pyrroles, as illustrated for instance by conversion of the readily available substrate 412 into the product 413 (Equation 117) <2005SC693>. 

It is highly probable that the initial step in the overmercaptalation of 27 involves formation of a 2,3-acyloxonium ion however, formation of the 1,2-episulfonium ion 28 as an intermediate in the replacement of the 2-hydroxyl group has been established130 through the conversion of 27 into 3,4,5,6-tetra-0-benzoyl-2-S-ethyl-2-thio-D-man-nose ethyl phenyl dithioacetal (34) by the action of benzenethiol and an acid catalyst. The presence of an ethylthio group on C-2 in 34 was further established by conversion of 34 into 3,4,5,6-tetra-O-benzoyl-2-S-ethyl-2-thio-D-mannose dimethyl acetal. 

Conversion of tetra-0-acetyl-/3-D-ribopyranose into methyl 1-thio-/3-D-ribopyranoside, by the action of methanethiol and zinc chloride, with subsequent deacetylation, is accompanied by the formation of substantial proportions of methyl l,5-dithio-j8-D-ribopyranoside (55) and 4-S-methyl-4-thio-L-lyxose dimethyl dithioacetal (53), plus a trace of 5-S-methyl-5-thio-D-ribose dimethyl dithioacetal (56). Although similar treatment of tetra-O-acetyl-jS-D-ribofuranose for a short time produced the expected methyl 1-thio-jS-D-... 

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